7-1 CHAPTER 7 The Reproductive Process

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-3 Nature of the Reproductive Process Reproduction is one of the most important properties of life Reproduction is one of the most important properties of life Two modes of reproduction Two modes of reproduction Asexual Asexual Sexual Sexual

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-5 Asexual Reproduction Asexual Reproduction Involves only one parent Involves only one parent No special reproductive organs or cells No special reproductive organs or cells Genetically identical offspring Genetically identical offspring Production of offspring is simple, direct, and rapid - increase population fast Production of offspring is simple, direct, and rapid - increase population fast Widespread in bacteria, unicellular eukaryotes and many invertebrate phyla Widespread in bacteria, unicellular eukaryotes and many invertebrate phyla Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-6 Asexual Reproductive Methods Asexual Reproductive Methods Binary Fission Binary Fission Common among bacteria and protozoa Common among bacteria and protozoa The parent divides by mitosis into two parts The parent divides by mitosis into two parts Each grows into an individual similar to the parent Each grows into an individual similar to the parent Multiple Fission Multiple Fission Nucleus divides repeatedly Nucleus divides repeatedly Cytoplasmic division produces many daughter cells Cytoplasmic division produces many daughter cells Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-7 Budding Budding Unequal division of an organism Unequal division of an organism Bud is an outgrowth of the parent Bud is an outgrowth of the parent Develops organs and then detaches Develops organs and then detaches Fragmentation Fragmentation Multicellular animal breaking into many fragments that become a new animal Multicellular animal breaking into many fragments that become a new animal Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-8 Sexual Reproduction Sexual Reproduction Generally involves two parents Generally involves two parents Special germ cells (gametes) unite to form a zygote Special germ cells (gametes) unite to form a zygote S exual reproduction recombines parental characters S exual reproduction recombines parental characters A richer, more diversified population results A richer, more diversified population results Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-9 Sexual Reproductive Methods Sexual Reproductive Methods Bisexual Reproduction Bisexual Reproduction Most common form Most common form Produces offspring from union of gametes from two genetically different parents Produces offspring from union of gametes from two genetically different parents Generally, individuals are male or female Generally, individuals are male or female Organisms are dioecious Organisms are dioecious Sexes are separate Sexes are separate Gonads (Found in most vertebrates and invertebrates) Gonads (Found in most vertebrates and invertebrates) Organs that produce gametes (testes, ovaries) Organs that produce gametes (testes, ovaries) Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The female produces the ovum The female produces the ovum Large with stored yolk and nonmotile Large with stored yolk and nonmotile Spermatozoa (sperm) are produced by the male Spermatozoa (sperm) are produced by the male Small, motile and much more numerous Small, motile and much more numerous Meiosis - used to make gametes Meiosis - used to make gametes Produces four haploid cells Produces four haploid cells Fertilization Fertilization Two haploid cells combine Two haploid cells combine Restores the diploid chromosome number in the zygote Restores the diploid chromosome number in the zygote Zygote divides by mitosis Zygote divides by mitosis Nature of the Reproductive Process

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hermaphroditism Hermaphroditism Both male and female organs in the same individual (monoeicious, hermaphrodites) Both male and female organs in the same individual (monoeicious, hermaphrodites) Many sessile, burrowing and/or endoparasitic invertebrates and some fish Many sessile, burrowing and/or endoparasitic invertebrates and some fish Most avoid self-fertilization Most avoid self-fertilization Exchange gametes with member of same species Exchange gametes with member of same species Each individual produces eggs, increases # Each individual produces eggs, increases # Hermaphroditic species could potentially produce twice as many offspring as dioecious species Hermaphroditic species could potentially produce twice as many offspring as dioecious species Sequential Hermaphroditism Sequential Hermaphroditism A genetically programmed sex change occurs with an individual organism A genetically programmed sex change occurs with an individual organism Ex: Clownfish - born male, change to female if dominant female is removed Ex: Clownfish - born male, change to female if dominant female is removed Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hermaphroditic Earthworms Mating

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Parthenogenesis Parthenogenesis Development of an embryo from an unfertilized egg Development of an embryo from an unfertilized egg Male and female nuclei fail to unite after fertilization Male and female nuclei fail to unite after fertilization Egg begins development without sperm Egg begins development without sperm Narrows the diversity available for adaptation to new conditions - not clones of female (haploid cells replicate) Narrows the diversity available for adaptation to new conditions - not clones of female (haploid cells replicate) Examples: fleas, bees, aphids, some fish and lizards Examples: fleas, bees, aphids, some fish and lizards Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Why do so many animals reproduce sexually rather than asexually? The costs of sexual reproduction are greater than asexual methods - negatives of sexual reproduction: The costs of sexual reproduction are greater than asexual methods - negatives of sexual reproduction: Requires more time Requires more time Uses more energy Uses more energy The cost of meiosis to the female involves passing only half of her genes to offspring The cost of meiosis to the female involves passing only half of her genes to offspring Production of males reduces resources for females that could produce eggs - more females = more offspring Production of males reduces resources for females that could produce eggs - more females = more offspring Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display However: Sexual organisms Sexual organisms Produce more diverse genotypes to survive in times of environmental change Produce more diverse genotypes to survive in times of environmental change diversity prevents extinction diversity prevents extinction On a geological time scale On a geological time scale Sexual lineages with less variation are prone to extinction Sexual lineages with less variation are prone to extinction Many invertebrates with both sexual and asexual modes enjoy the advantages of both Many invertebrates with both sexual and asexual modes enjoy the advantages of both Example: Starfish, Lizard Example: Starfish, Lizard Nature of the Reproductive Process

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Unisex - ALL female lizardsBisexual - Both Male and Female Present

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sex Determination Sex Determination At first, gonads are sexually identical At first, gonads are sexually identical In human males In human males SRY (sex determining region Y) on the Y chromosome organizes the gonad into a testis SRY (sex determining region Y) on the Y chromosome organizes the gonad into a testis Once formed, the testis Once formed, the testis Secretes testosterone which, masculinizes the fetus Secretes testosterone which, masculinizes the fetus Development of a penis, scrotum and male ducts, and glands Development of a penis, scrotum and male ducts, and glands Females have no “Y”, so gonads never change into testes, therefore Testosterone is never secreted Females have no “Y”, so gonads never change into testes, therefore Testosterone is never secreted Sex Determination

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Absence of testosterone in a genetic female embryo Absence of testosterone in a genetic female embryo Promotes development of female sexual organs Promotes development of female sexual organs Vagina, clitoris and uterus Vagina, clitoris and uterus Genetics of sex determination vary: Genetics of sex determination vary: XX-XY XX-XY Haplodiploid (males are formed from unfertilized eggs) XX-XO Haplodiploid (males are formed from unfertilized eggs) XX-XO Temperature Temperature Sex Determination

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Incubation Temperature determine sex of offspring

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Gametogenesis Gametogenesis Gametes formation Gametes formation Spermatogenesis (Testes) Spermatogenesis (Testes) Oogenesis (Ovaries) Oogenesis (Ovaries) Germ Cells

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Seminiferous Tubule containing sperm

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Spermatogenesis Spermatogenesis Formation of sperm Formation of sperm Parts of Sperm Parts of Sperm Haploid nucleus condenses into a head Haploid nucleus condenses into a head A midpiece forms containing mitochondria A midpiece forms containing mitochondria The whiplike flagellar tail provides locomotion The whiplike flagellar tail provides locomotion Sperm head contains an acrosome Sperm head contains an acrosome Often contains enzymes to aid in penetration of egg layers Often contains enzymes to aid in penetration of egg layers Enzymes are specific to a species. Why?? Enzymes are specific to a species. Why?? Germ Cells

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Acrosome produces specific enzymes, so they only digest their species’ egg’s membrane. This helps aquatic animals who might spawn at the same time. Ex. Coral sperm can’t fertilize Sea Star eggs.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Oogenesis Oogenesis Formation of ovum (egg) - 3 polar bodies and 1 egg Formation of ovum (egg) - 3 polar bodies and 1 egg Germ Cells

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Reproductive Patterns Reproductive Patterns Oviparous (“egg-birth”) Animals Oviparous (“egg-birth”) Animals Lay eggs outside the body Lay eggs outside the body Fertilization may be internal (before eggs are laid) or external (after laid) Fertilization may be internal (before eggs are laid) or external (after laid) Some animals abandon eggs; others provide extensive care Some animals abandon eggs; others provide extensive care Examples: reptiles, birds, amphibians, fish Examples: reptiles, birds, amphibians, fish TYPES OF BIRTH

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Ovoviviparous (“egg-live-birth”) Animals Ovoviviparous (“egg-live-birth”) Animals Retain eggs in their body Retain eggs in their body Essentially all nourishment is derived from the yolk not the mother. Essentially all nourishment is derived from the yolk not the mother. Fertilization is internal Fertilization is internal Common in some invertebrate groups and aquatic animals, certain fishes (sharks) and reptiles Common in some invertebrate groups and aquatic animals, certain fishes (sharks) and reptiles Reproductive Patterns Reproductive Patterns

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Viviparous (“live-birth”) Animals Viviparous (“live-birth”) Animals Give birth to young in a more advanced stage of development Give birth to young in a more advanced stage of development Eggs develop in oviduct or uterus Eggs develop in oviduct or uterus Embryos continuously derive nourishment from the mother Embryos continuously derive nourishment from the mother Fertilization is internal Fertilization is internal Occurs in mammals and some fishes Occurs in mammals and some fishes Provides more protection to offspring Provides more protection to offspring Reproductive Patterns Reproductive Patterns

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Invertebrate Reproductive Systems Invertebrate Reproductive Systems Invertebrates that transfer sperm for internal fertilization require complex organs Invertebrates that transfer sperm for internal fertilization require complex organs Insects (Crickets) - have an ovipositor - helps deposit eggs Insects (Crickets) - have an ovipositor - helps deposit eggs Plan of Reproductive Systems Plan of Reproductive Systems

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Crickets’ Sex Organs Sperm is stored in a sac (spermatophore) and deposited into the genital bursa of the female. The female then controls the release of a few sperm to fertilize her eggs at the moment they are laid, using the ovipositor.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Vertebrate Reproductive Systems Vertebrate Reproductive Systems Reproductive and excretory systems are called the urogenital system Reproductive and excretory systems are called the urogenital system Close anatomical connection Close anatomical connection In male fishes and amphibians In male fishes and amphibians In all vertebrates except most mammals In all vertebrates except most mammals Ducts open into a cloaca Ducts open into a cloaca In females with cloacas, the oviduct also opens into cloaca In females with cloacas, the oviduct also opens into cloaca Most female mammals have separate excretory and reproductive systems Most female mammals have separate excretory and reproductive systems Plan of Reproductive Systems Plan of Reproductive Systems

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Female Reproductive Parts: Vagina, Ovary, Cervix, Fallopian Tubes Male Reproductive Parts: Scrotum, Testis, Epididymis, Vas deferens, Prostate, Seminal Vesicles, Urethra, Penis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Endocrine Events that Orchestrate Reproduction Hormonal Control of Timing of Reproductive Cycles Hormonal Control of Timing of Reproductive Cycles Vertebrate reproduction Vertebrate reproduction Seasonal or cyclic Seasonal or cyclic Offspring arrive when food is available and other environmental conditions are optimal for survival Offspring arrive when food is available and other environmental conditions are optimal for survival Sexual cycles Sexual cycles Controlled by hormones that respond to food intake, photoperiod, rainfall, temperature or social cues Controlled by hormones that respond to food intake, photoperiod, rainfall, temperature or social cues Hypothalamus controls release of hormones Hypothalamus controls release of hormones

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Multiple Births Multiple Births Many animals are multiparous Many animals are multiparous Give birth to many offspring at one time Give birth to many offspring at one time Some are uniparous (elephants) Some are uniparous (elephants) Give birth only to one at a time Give birth only to one at a time Exceptions occur Exceptions occur Armadillos gives birth to four young, all male or all female Armadillos gives birth to four young, all male or all female Derived from one zygote - IDENTICAL Derived from one zygote - IDENTICAL Childbirth

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Identical Twins - separate Identical Twins - separate One-third have separate placentas and amniotic sacs One-third have separate placentas and amniotic sacs Indicates fertilized egg separated at an early stage Indicates fertilized egg separated at an early stage Two-thirds share a placenta with separate amniotic sac Two-thirds share a placenta with separate amniotic sac Splitting occurred after implantation Splitting occurred after implantation A few share 1 amniotic sac and 1 placenta A few share 1 amniotic sac and 1 placenta Indicates that separation of the zygote occurred after day 9 of pregnancy, when the amnion has formed Indicates that separation of the zygote occurred after day 9 of pregnancy, when the amnion has formed These twins risk becoming conjoined (Siamese twinning) These twins risk becoming conjoined (Siamese twinning) Endocrine Events that Orchestrate Reproduction

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display /3 2/3 Rare - possible Conjoined twins